Budapest, Hungary
Budapest, Hungary

Time filter

Source Type

De Ugarte Postigo A.,National institute for astrophysics | De Ugarte Postigo A.,European Southern Observatory | Horvath I.,Bolyai Military University | Veres P.,Bolyai Military University | And 19 more authors.
Astronomy and Astrophysics | Year: 2010

Context. Gamma-ray bursts are usually classified in terms their high-energy emission into either short-duration or long-duration bursts, which presumably reflect two different types of progenitors. However, it has been shown on statistical grounds that a third, intermediate population is needed in this classification scheme, although an extensive study of the properties of this class has so far not been performed. The large amount of follow-up studies generated during the Swift era allows us to have a sufficient sample to attempt a study of this third population through the properties of their prompt emission and their afterglows. Aims. To understand the differences of the intermediate population, we study a sample of GRBs observed by Swift during its first four years of operation. The sample contains only bursts with measured redshifts since these data help us to derive intrinsic properties. Methods. We search for differences in the properties of the three groups of bursts, which we quantify using a Kolmogorov-Smirnov test whenever possible. Results. Intermediate bursts are found to be less energetic and have dimmer afterglows than long GRBs, especially when considering the X-ray light curves, which are on average one order of magnitude fainter than long bursts. There is a less significant trend in the redshift distribution that places intermediate bursts closer than long bursts. Except for this, intermediate bursts show similar properties to long bursts. In particular, they follow the Epeak versus Eiso correlation and have, on average, positive spectral lags with a distribution similar to that of long bursts. As for long GRBs, they normally have an associated supernova, although some intermediate bursts have been found to contain no supernova component. Conclusions. This study shows that intermediate bursts differ from short bursts, but exhibit no significant differences from long bursts apart from their lower brightness. We suggest that the physical difference between intermediate and long bursts could be explained by being produced by similar progenitors, of the former being the ejecta thin shells and the latter thick shells. © 2010 ESO.


Ripa J.,Charles University | Ripa J.,Ewha Womans University | Meszaros A.,Charles University | Veres P.,Pennsylvania State University | And 4 more authors.
Astrophysical Journal | Year: 2012

A sample of 427 gamma-ray bursts (GRBs) from a database (2002 February-2008 April) of the RHESSI satellite is analyzed statistically. The spectral lags and peak-count rates, which have been calculated for the first time in this paper, are studied, completing an earlier analysis of durations and hardness ratios. The analysis of the RHESSI database has already inferred the existence of a third group with intermediate duration, apart from the so-called short and long groups. The first aim of this article is to discuss the properties of these intermediate-duration bursts in terms of peak-count rates and spectral lags. The second aim is to discuss the number of GRB groups using another statistical method and by also employing the peak-count rates and spectral lags. The standard parametric (model-based clustering) and non-parametric (K-means clustering) statistical tests together with the Kolmogorov-Smirnov and Anderson-Darling tests are used. Two new results are obtained. (1) The intermediate-duration group has properties similar to those of the group of short bursts. Intermediate and long groups appear to be different. (2) The intermediate-duration GRBs in the RHESSI and Swift databases seem to be represented by different phenomena. © © 2012. The American Astronomical Society. All rights reserved..


Veres P.,A.P.S. University | Veres P.,Bolyai Military University | Bagoly Z.,A.P.S. University | Horvath I.,Bolyai Military University | And 2 more authors.
Astrophysical Journal | Year: 2010

Gamma-ray bursts (GRBs) are the most luminous events in the universe. Going beyond the short-long classification scheme, we work in the context of three burst populations with the third group of intermediate duration and softest spectrum.We are looking for physical properties which discriminate the intermediate duration bursts from the other two classes. We use maximum likelihood fits to establish group memberships in the duration-hardness plane. To confirm these results we also use k-means and hierarchical clustering. We use Monte Carlo simulations to test the significance of the existence of the intermediate group and we find it with 99.8% probability. The intermediate duration population has a significantly lower peak flux (with 99.94% significance). Also, long bursts with measured redshift have higher peak fluxes (with 98.6% significance) than long bursts without measured redshifts. As the third group is the softest, we argue that we have related them with X-ray flashes among the GRBs. We give a new, probabilistic definition for this class of events. © 2010. The American Astronomical Society. All rights reserved.


Veres P.,Eötvös Loránd University | Veres P.,Bolyai Military University | Bagoly Z.,Eötvös Loránd University | Horvath I.,Bolyai Military University | And 3 more authors.
AIP Conference Proceedings | Year: 2010

Swift satellite measurements contributed substantially to the gamma-ray burst (GRB) redshift observations through fast slewing to the source of the GRBs. Still, a large number of bursts are without redshift. We study the celestial distribution of bursts with various methods and compare them to a random catalog using Monte-Carlo simulations. We find an anisotropy in the distribution of the intermediate class of bursts and find that the short and long population are distributed isotropically. © 2010 American Institute of Physics.


Horavth I.,Bolyai Military University | Bagoly Z.,A.P.S. University | Balazs L.G.,Konkoly Observatory | De Ugarte Postigo A.,European Southern Observatory | And 4 more authors.
Astrophysical Journal | Year: 2010

Earlier classification analyses found three types of gamma-ray bursts (short, long, and intermediate in duration) in the BATSE sample. Recent works have shown that these three groups are also present in the RHESSI and BeppoSAX databases. The duration distribution analysis of the bursts observed by the Swift satellite also favors the three-component model. In this paper, we extend the analysis of the Swift data with spectral information. We show, using the spectral hardness and duration simultaneously, that the maximum likelihood method favors the three-component against the two-component model. The likelihood also shows that a fourth component is not needed. © 2010 The American Astronomical Society. All rights reserved.


Balazs L.G.,Konkoly Observatory | Veres P.,Eötvös Loránd University | Veres P.,Bolyai Military University
Advances in Space Research | Year: 2011

We propose to study the interrelation between the γ- (Fluence, 1sec Peakflux, duration) and X-ray (early X flux, 24 h X flux, X decay index, X spectral index, X HI column density) properties using the canonical correlation method. Computing the canonical correlations and variables we show that there is a significant interrelation between the γ- and X-ray data. Using the canonical variables from the analysis, we computed their correlations (canonical loadings) with the original ones. The canonical loadings revealed that the γ-ray fluence and the early X-ray flux give the strongest contribution to the correlation in contrast to the X-ray decay index and spectral index. An interesting new result appears to be the strong contribution of the HI column density to the correlation. Accepting the collapsar model of long GRBs this effect may be interpreted as an indication for the ejection of an HI envelope by the progenitor in the course of producing the GRB. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.


Tello J.C.,Institute Astrofisica Of Andalucia Iaa Csic | Castro-Tirado A.J.,Institute Astrofisica Of Andalucia Iaa Csic | Gorosabel J.,Institute Astrofisica Of Andalucia Iaa Csic | Perez-Ramirez D.,University of Jaén | And 6 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Since the early 1990s, gamma ray bursts (GRB) have been accepted to be of extra-Galactic origin because of the isotropic distribution observed by BATSE and the redshifts observed via absorption line spectroscopy. Nevertheless, upon closer examination at least one case turned out to be of Galactic origin. This particular event presented a fast rise and exponential decay (FRED) structure, which leads us to believe that other FRED sources might also be Galactic. Aims. This study was set out to estimate the most probable degree of contamination by Galactic sources that certain samples of FREDs have. Methods. To quantify the degree of anisotropy, the average dipolar and quadripolar moments of each sample of GRBs with respect to the Galactic plane were calculated. This was then compared to the probability distribution of simulated samples comprising a combination of isotropically generated sources and Galactic sources. Results. We observe that the dipolar and quadripolar moments of the selected subsamples of FREDs are found more than two standard deviations outside those of random isotropically generated samples. The most probable degree of contamination by Galactic sources for the FRED GRBs of the Swift catalog detected until February 2011 that do not have a known redshift is about 21 out of 77 sources, which represents roughly 27%. Furthermore, we observe that by removing from this sample those bursts that have any type of indirect redshift indicator and multiple peaks, the most probable contamination increases to 34% (17 out of 49 sources). Conclusions. It is probable that a high degree of contamination by Galactic sources occurs among the single-peak FREDs observed by Swift. Accordingly, we encourage additional studies on these types of events to determine the nature of what could be an exotic type of Galactic source. © ESO, 2012.


Bagoly Z.,Eötvös Loránd University | Veres P.,Eötvös Loránd University | Veres P.,Bolyai Military University
AIP Conference Proceedings | Year: 2010

We propose a search for lensed candidates using an achromatic cross-correlation method, by looking at bursts days to years apart coming from approximately the same part of the sky. We use gamma-ray burst data from Fermi spacecraft. We search for 'repeating' bursts, which would be the lensed manifestation of the same event seen days or months apart. A lensed pair would enable us to constrain the mass and the gravitational potential structure of the lensing object. © 2010 American Institute of Physics.


Veres P.,Eötvös Loránd University | Veres P.,Bolyai Military University
Advances in Space Research | Year: 2011

The amount of data on gamma-ray bursts (GRBs) and the detected afterglows observed by the Swift satellite contributed significantly to the understanding of the phenomenon. The behavior of the early afterglow rises some interesting questions. With the early afterglow localizations of gamma-ray burst positions made by Swift, the clear delimitation of the prompt phase and the afterglow is not so obvious any more. There are hints of a canonical X-ray afterglow lightcurve with segments of different slopes. Not all bursts necessarily show all the segments. It is important to see if the prompt phase and the afterglow has the same origin or they stem from different parts of the progenitor system. We will combine the of gamma-ray burst data from BAT and XRT and compare the extrapolated gamma-ray flux to the X-ray in a sample of bursts and find that there is a good agreement between the two measurements. This indicates that the physical process shaping burst and the early afterglow are the same. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.


Szecsi D.,Eötvös Loránd University | Szecsi D.,MTA CSFK Konkoly Observatory | Szecsi D.,University of Bonn | Bagoly Z.,Eötvös Loránd University | And 5 more authors.
Astronomy and Astrophysics | Year: 2013

Context. We present a method for determining the background of the gamma-ray bursts (GRBs) of the Fermi Gamma-ray Burst Monitor (GBM) using the satellite positional information and a physical model. Since the polynomial fitting method typically used for GRBs is generally only indicative of the background over relatively short timescales, this method is particularly useful in the cases of long GRBs or those that have autonomous repoint request (ARR) and a background with much variability on short timescales. Aims. Modern space instruments, like Fermi, have some specific motion to survey the sky and catch gamma-ray bursts in the most effective way. However, GBM bursts sometimes have highly varying backgrounds (with or without ARR), and modelling them with a polynomial function of time is not efficient-one needs more complex, Fermi-specific methods. This article presents a new direction dependent background fitting method and shows how it can be used for filtering the lightcurves. Methods. First, we investigate how the celestial position of the satellite may have influence on the background and define three underlying variables with physical meaning: celestial distance of the burst and the detector's orientation, the contribution of the Sun and the contribution of the Earth. Then, we use multi-dimensional general least square fitting and Akaike model selection criterion for the background fitting of the GBM lightcurves. Eight bursts are presented as examples, of which we computed the duration using background fitted cumulative lightcurves. Results. We give a direction dependent background fitting (DDBF) method for separating the motion effects from the real data and calculate the duration (T90, T50, and confidence intervals) of the nine example bursts, from which two resulted an ARR. We also summarize the features of our method and compare it qualitatively with the official GBM Catalogue. Conclusions. Our background filtering method uses a model based on the physical information of the satellite position. Therefore, it has many advantages compared to previous methods. It can fit long background intervals, remove all the features caused by the rocking behaviour of the satellite, and search for long emissions or not-triggered events. Furthermore, many parts of the fitting have now been automatised, and the method has been shown to work for both sky survey mode and ARR mode data. Future work will provide a burst catalogue with DDBF. © 2013 ESO.

Loading Bolyai Military University collaborators
Loading Bolyai Military University collaborators